The term ‘phase change materials’ (PCMs) refers to substances with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as latent heat storage (LHS) units.
PCM's latent heat storage can be achieved through solid-solid, solid-liquid, solid-gas and liquid-gas phase change. However, the only phase change used for PCMs is the solid-liquid change.
Initially, the solid-liquid PCMs behave like sensible heat storage (SHS) materials; their temperature rises as they absorb heat. Unlike conventional SHS, however, when PCMs reach the temperature at which they change phase (their melting temperature commonly referred to as the ‘set point’) they absorb large amounts of heat at an almost constant temperature. The PCM continues to absorb heat without a significant rise in temperature until all the material is transformed to the liquid phase. When the ambient temperature around the liquid PCM falls, the PCM solidifies, releasing its stored latent heat.
A large number of PCMs are commercially available in any required temperature range from −5 up to 190° C. Within the human comfort range between 20-30° C., some PCMs are very effective at stabilizing daily internal temperature fluctuations. PCMs store 5 to 14 times more heat per unit volume than conventional storage materials such as water, masonry or stone. One application for PCMs is their use in buildings to modulate temperature variations, and thereby reduce energy consumption, or to shift energy consumption to off-peak load times. In such applications, the PCMs are generally placed out of view, such as within the wall cavity or in the ceiling. Such placement reduces the exposure of the PCM to air flow within the living/working space, and also hides the operation and functionality of the PCMs from the building occupants. One aspect of the present invention is therefore to describe devices for containment of PCMs that are designed to be directly exposed to air flow. Another aspect of the present invention is to describe devices for containment of PCMs that are designed to enable building occupants to be visually aware of the operations and functionality of the PCMs such that occupants can reconfigure them for more effective internal temperature stabilization. Yet another aspect of the invention is to provide a variety of stand-alone systems (not integrally connected to building infrastructure) that enable building occupants to vary the distribution and set point (freeze/melt) of PCM within room based on their experience of thermal comfort and the visual cues enabled by the device design.